Drop detection

Abstract

Herein is described a method involving a drop detector. The method may comprise: ejecting ink drops from the nozzles on a printhead toward a drop detector. A drop characteristic may then be determined from the drop detector for each ink-jet nozzle. Drop characteristics for the nozzles across the printhead may be collated into a data set, and compared with a predetermined data set for a printhead having predetermined print behaviour to determine if and how the data sets differ in terms of the pattern of drop characteristics across the printheads. If the data sets differ, a recovery strategy may be selected based how the data sets differ in terms of the pattern of drop characteristics across the printheads. A system and computer readable medium are also described herein.

The invention claimed is: 
     
       1. A method comprising:
 ejecting ink from a plurality of ink-jet nozzles on a printhead, such that ink drops are ejected from the nozzles toward a drop detector; 
 determining a drop characteristic from the drop detector for each ink-jet nozzle; 
 collating the drop characteristics for the nozzles across the printhead into a data set; 
 comparing the data set from the printhead with a predetermined data set for a printhead having predetermined print behaviour to determine if and how the data sets differ in terms of the pattern of drop characteristics across the printheads; and, 
 if the data sets differ,
 selecting a recovery strategy based how the data sets differ in terms of the pattern of drop characteristics across the printheads; and 
 implementing the recovery strategy to alter the ejection behaviour of at least some of the nozzles on the printhead. 
 
 
     
     
       2. The method according to  claim 1 , wherein the drop characteristic for each ink-jet nozzle is at least one of drop velocity, length of time from drop ejection to detection, drop size, drop shape, the rate of drops ejected per second and color of the drops. 
     
     
       3. The method according to  claim 1 , wherein the comparing involves determining the proportion of nozzles of the printhead that shows a drop characteristic that is different from the drop characteristic of the printhead having predetermined print behaviour. 
     
     
       4. The method according to  claim 3 , wherein, if above a pre-determined proportion of nozzles of the printhead shows a drop velocity that is different from the drop velocity of the printhead having predetermined print behaviour, the printhead has its alignment adjusted as a recovery strategy to compensate for the difference in drop velocities. 
     
     
       5. The method according to  claim 3 , wherein if below a pre-determined proportion of nozzles of the printhead show a drop velocity that is lower than the drop velocity of the printhead having predetermined print behaviour, the energy supplied to the nozzles having this lower drop velocity is increased for the subsequent drop ejection. 
     
     
       6. The method according to  claim 5 , wherein the ejection behaviour of the printhead is tested to determine if the drop velocity for the nozzles previously showing the lower drop velocity has been corrected. 
     
     
       7. The method according to  claim 5 , wherein the increased energy is supplied only for a specific period of time so as to clean the nozzles. 
     
     
       8. The method according to  claim 1 , wherein the comparing involves comparing a data set represented by a graph that plots the drop characteristics over time along the y-axis, against each nozzle along the printhead along the x-axis. 
     
     
       9. The method according to  claim 8 , wherein the comparing involves comparing the shape of the graph against the shape of a corresponding graph for the printhead having predetermined print behaviour. 
     
     
       10. The method according to  claim 8 , wherein the drop characteristic for each nozzle is selected from drop velocity and length of time from drop ejection (or a certain time point from ejection) to detection. 
     
     
       11. A system comprising:
 a printhead having a plurality of ink-jet nozzles, 
 a drop detector, 
 a controller to control the ejection of ink from the ink-jet nozzles on the printhead, such that ink drops are ejected from the plurality of nozzles toward a drop detector, and 
 a processor to (i) collate drop characteristics from the drop detector for nozzles across the printhead into a data set, and (ii) compare the data set from the printhead with a predetermined data set for a printhead having predetermined print behaviour to determine if and how the data sets differ in terms of the pattern of drop characteristics across the printheads; and (iii), if the data sets differ, the processor selects a recovery strategy based how the data sets differ in terms of the pattern of drop characteristics across the printheads, the processor sending a signal to the controller to implement the recovery strategy to alter the ejection behaviour of at least some of the nozzles on the printhead. 
 
     
     
       12. The system according to  claim 11 , wherein the drop characteristic for each nozzle is at least one of drop velocity, length of time from drop ejection to detection, drop size, drop shape, the rate of drops ejected per second and color of the drops. 
     
     
       13. The system according to  claim 11 , when the processor compares the data set from the printhead with a predetermined data set for a printhead having predetermined print behaviour, this involves determining the proportion of nozzles of the printhead that show a drop characteristic that is different from the drop characteristic of the printhead having predetermined print behaviour. 
     
     
       14. The system according to  claim 13 , wherein, if above a pre-determined proportion of nozzles of the printhead show a drop velocity that is different from the drop velocity of the printhead having predetermined print behaviour, the processor sends a signal to the controller to implement the recovery strategy, which comprises adjusting the alignment of the printhead to compensate for the difference in drop velocities. 
     
     
       15. The system according to  claim 13 , wherein if below a pre-determined proportion of nozzles of the printhead show a drop velocity that is lower than the drop velocity of the printhead having predetermined print behaviour, the energy supplied to the nozzles having this lower drop velocity is increased for the subsequent drop ejection. 
     
     
       16. The system according to  claim 15 , wherein the increased energy is supplied only for a specific period of time so as to clean the nozzles. 
     
     
       17. A computer readable medium having instructions stored thereon that, if executed by a processor, cause the processor to:
 collate drop characteristics for nozzles across a printhead into a data set; 
 compare the data set from the printhead with a predetermined data set for a printhead having predetermined print behaviour to determine if and how the data sets differ in terms of the pattern of drop characteristics across the printheads; and, 
 if the data sets differ,
 select a recovery strategy based how the data sets differ in terms of the pattern of drop characteristics across the printheads; and 
 implement the recovery strategy to alter the ejection behaviour of at least some of the nozzles on the printhead. 
 
 
     
     
       18. The computer readable medium according to  claim 17 , wherein the comparing involves determining the proportion of nozzles of the printhead that shows a drop characteristic that is different from the drop characteristic of the printhead having predetermined print behaviour. 
     
     
       19. The computer readable medium according to  claim 18 , wherein, if above a pre-determined proportion of nozzles of the printhead shows a drop velocity that is different from the drop velocity of the printhead having predetermined print behaviour, the printhead has its alignment adjusted as a recovery strategy to compensate for the difference in drop velocities. 
     
     
       20. The computer readable medium according to  claim 18 , wherein if below a pre-determined proportion of nozzles of the printhead show a drop velocity that is lower than the drop velocity of the printhead having predetermined print behaviour, the energy supplied to the nozzles having this lower drop velocity is increased for the subsequent drop ejection.